Hydrocarbon well logging



, June 4, 1968 o. T. MOORE 3,

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Filed March 18. 1966 INVENTOR. CLAN T. MOORE BY M 4M ATTORNEYS UnitedStates Patent 3,386,286 HYDROCARBON WELL LOGGING Olan T. Moore, P.O. Box3297, Midland, Tex. 79701 Filed Mar. 18, 1966, Ser. No. 535,423 7Claims. (Cl. 73-153) ABSTRACT OF THE DISCLOSURE A hydrocarbon welllogging method which includes, in addition to the usual depthmeasurements, mud flow measurement and detection of hydrocarbon gases inthe diverted portion of the mud, the steps of measuring the total flowrate of mud, the flow rate of diverted mud and correlatively recordingthe total relative amount of gas for the mud flowing through incrementsof the well bore, in order to obtain the relative gas content of eachvolumetric increment of the formation through which the well is drilled.In addition the relative amount of total methane, ethane and propane, aswell as the relative amount of normal butane, isobutane, normal pentaneand isopentane may be recorded.

This invention relates to hydrocarbon well logging.

In the normal drilling of an oil or gas well, a drill bit, which isrotated by a drill string, bores 21 hole downwardly through successiveformations, until one or more oil or gas producing zones areencountered, or the well is abandoned. A mixture, as of water or oil andother ingredients, which forms a mud, is normally circulated down thedrill string, out through the bit and then up the hole, although undercertain circumstances, a reverse circulation, i.e., passing the mud downthe hole and back up through the drill string, may be utilized. The mudnot only lubricates the drill bit, but also provides a sufficientpressure to prevent oil or gas under pressure encountered in a lowerformation from blowing the mud out of the well, or salt water or thelike from flowing into the well. Sometimes, the mud seals off aproducing formation, so that such a formation may be difficult todetect. An experienced driller can often tell by the resistance todrilling the general type of formation encountered, while the cuttings,which are small particles of the formation reduced in size by the drillbit and carried up the hole by the mud, give an indication of thelithology or type of formation encountered. Oftentimes, when a formationwhich is suspected of being oil or gas producing is encountered, a coreis taken, so that the actual formation may be more accuratelydetermined.

Since the geologist or other person in charge of drilling the wellcannot be personally at the bottom of the well and either observe ortest the formation being drilled through, it is necessary that allavailable information indicative of the presence of an oil or gasproducing zone be made available. Such information is never conclusiveof the presence of an oil or gas producing zone, so that the greater theamount of information available, the greater the possibility of aproducing zone being identified. If a producing zone is suspected, adrill stem test is sometimes made, in which the mud pressure is reduced,so that oil or gas in a suspected producing zone will have anopportunity to escape into the well and come to the surface. There are,of course, various well known stratagems, primarily involving packers,by which a section of the well may be isolated for such a drill sterntest.

One way in which a considerable amount of information about thecharacter and propensities of the formations drilled through may beobtained is by electric logging, involving the lowering of an instrumentdown the well, by which successive portions of the well bore wall aresubjected to electrical resistivity tests, gamma ray tests, neutrontests, sonic tests and the like. However, the lowering of such aninstrument in the well requires that the drill string be removed fromthe well and thus can ordinarily be made only when the bit is changed orcasing is to be installed, without otherwise interrupting the drillingoperation. Electric logs are commonly run just before casing is set, asat 5,000 it, before the size of the drill bit is reduced, again at12,000 ft. or a higher elevation, if the bit size is changed, andfinally when the bottom of the hole is reached. Since the gamma ray andneutron logs can be run with casing in the well, but other electric logscannot, it is desirable to run electric logs without casing in theportion being logged. Even in an exploratory or wildcat well, suchelectrical logs are usually made at the same depths. In a wildcat well,the formations encountered are generally unknown, even though thegeneral contour and general depth of various formation layers may havebeen reasonably established through geophysical methods. Drill stemtests are thus more frequently used than electric logs are run and have,in the past, usually been run whenever there is an indication of ahydrocarbon producing zone. Previous hydrocarbon logs would indicate theapparent production of hydrocarbon gases, and any sudden increase or gaskick would suggest the possibility of a hydrocarbon producing zone.However, when previously produced gas is already present in the mudstream, it is sometimes diflicult to determine whether a change in thetotal gas, for instance, is due to new gas in the mud or some otherfactor. Thus, it is desirable to have a more reliable indicator whichwill eliminate unnecessary drill stem tests and also suggest otherswhich are actually desirable.

In hydrocarbon well logging, it is unnecessary to remove the drill bitfrom the well, so that a decided advantage of such logging is the factthat it may be carried out simultaneously with the drilling operation.The depth at which the drill is operating is, of course, determined bythe length of the drill string, and this is readily measured andrecorded in a known manner. As the drill progresses further down thehole, the time required for the mud to reach the bottom of the hole, aswell as flow up the hole, increases. The inside diameter of the drillstring is known, so that the time for the mud to proceed from the top ofthe well to the 'bit may be calculated from the known volume of mudbeing pumped down the well. Due to the fact that the formations drilledthrough do not always retain the borehole size produced by the bit, dueto sloughing or caving of softer formations and the size of the borechanges when a smaller bit is used, the time required for the mud orcuttings to proceed from the drill bit to the top of the well is notalways proportional to the ratio between the diameter of the drill bitand the inside diameter of the drill string. However, a dye or othertype of marker may be placed in the mud stream and timed from itsentrance therein to its discharge from the well, then the calculatedtime for the mud to proceed down the drill stem may be subtracted, inorder to arrive at the lag time, i.e., the amount of time representingthe difference between the discharge of mud from the bit, including theproduction of cuttings accompanying the mud, and the time at which thismud and the cuttings carried thereby reaches the surface. Of course, anysloughing or caving will normally occur considerably above the drillbit, so that this factor is not detrimental to the method of thisinvention, as will hereinafter appear.

In hydrocarbon well logging, e.g., US. Patent 2,214,- 674, a portion ofthe mud may be treated to remove the occluded gas therein and the gasmixed with air and tested, as by a so-called hot wire gas detector,e.g.,

U.S. Patent 2,489,180, for the relative amount of gas therein. Such ahot wire detector has thus been known and used for a number of years,while a more recent development, the gas chromatograph enables the gasto be tested for individual constituents thereof, such as methane,ethane, propane, n-butane, isobutane, npentane, isopentane and the like.The gas chromatograph is a highly desirable instrument which providesconsiderable information, yet operates relatively slowly, so that thegas test can be made on a specimen only at longer intervals of time,such as six minutes apart, whereas the hot wire detector providessubstantially instantaneous readings. The gas chromatograph is usuallyset to provide automatically a test every feet, or perhaps a lessernumber of feet, although it can be manually actuated at any time. Inaddition to testing the mud for gas, samples of the cuttings carried bythe mud may be separated therefrom successively and also tested for gasin a known manner, while both the mud and the cuttings may be tested forthe presence of oil, as through the observance thereof under ultravioletlight. Also, the cuttings may be subjected to a vacuum, to cause any oilor gas therein to be sucked therefrom and observed under a microscope,e.g., U.S. Patent 2,756,585. The cuttings are also examined to determinethe character of the formation from which the cuttings came. All ofthese tests, of course, increase the knowledge about the formation beingdrilled through, or actually the formation which was drilled through atthe time the well was at the depth indicated by the lag time, whichassists the geologist in determining whether a potential oil or gasproducing zone has been encountered.

It has been a generally accepted theory for a number of years that theonly gas or oil contained in the cuttings comes from the cylinder of theformation chewed up by the bit and that the cuttings lose such gas oroil into the mud, as they proceed up the borehole. It is also agenerally accepted theory that, in general, the mud carries the cuttingsand the gas it receives up the well in approximately the same order inwhich the cuttings were produced by the drill bit, although it has beendefinitely established that the cuttings are not carried upwardly by themud in precisely the same order in which they were produced from theformation, but that there is a longitudinal intermixing of the cuttings.For instance, if a strata of linestone, with shale both above and below,is drilled through, shale cuttings intermixed with limestone cuttingsWill be discharged at the top of the well for a period of time after thelag time indicates that the drill is progressing through limestone only.Also, limestone cuttings will appear intermixed with the shale cuttingsfor a period of time after the drill has passed from the limestone intothe shale beneath. This factor is not of considerable importance whenthe various formations are relatively thick, but when the layers orformations are only a few feet thick, particularly when one of them is aproducing formation, such intermixing of the cuttings may be ofconsiderable significance.

Hydrocarbon logs, are, in essence, data sheets giving, for increments ofdepth of the well, such information as the drilling rate, the lithologyas determined by the cuttings, the relative amounts of gas separatedfrom the mud, either determined by the hot wire gas detector or the gaschromatograph, of both, the relative amounts of .gas detected uponremoval from the cuttings, such as the total gas or gas constituents,and other data, including where drill stem tests were made, where coreswere taken, the specific gravity or weight of the mud, the constituentsused to make up the mud, and the results of tests of the mud for pH,salinity and the like. When a gas chromatograph is utilized, either therelative amounts of the constituent gases may be plotted in curves, suchas one curve for each as, or the total detection of methan, ethane andpropane as one curve, and the total detection of butanes and pentanes,both normal and iso, as another curve. The significance of these gascurves it that, if there is a sudden increase in the total gas, this isan indication that a formation, from Which the mud or cuttings involvedcame, may be suspected of being an oil or gas producing zone. Also anaccompanying sudden increase of the butanes and propanes is indicativeof a suspicion that the suspected roducing zone may be an oil producin gzone.

Notwithstanding the considerable and valuable information which ahydrocarbon well log furnishes the geologist, there are at least twoareas in which no procedure heretofore developed has been able tofurnish any specific information. The first is the detection ofrelatively narrow or shallow formations which are possibly oil or gasproducing, and the second is a correlation of one or more curves of thehydrocarbon Well log with the curves from electrical logging.

Among the objects of this invention are to provide a novel method ofhydrocarbon well logging; to provide such a method which provides moreaccurate information relating to the possibility of an oil or gasproducing strata, particularly a narrow or shallow oil or gas producingstrata; to provide such a method by which a hydrocarbon well log may beproduced which provides additional information to a geologist; toprovide such a method which produces a hydrocarbon well log which ismore nearly correlated with an electrical log made in the same well; toprovide such a method which may be utilized in producing a hydrocarbonwell log without requiring the drill bit and drill stem to be removedfrom the well; to provide such a method which may be carried outsimultaneously with the drilling of the well and which thus providesadditional information about the formation being drilled through,corresponding to but before an electrical log can be made; to providesuch a method which will tend to eliminate unnecessary drill stem testsand suggest those which are actually desirable; and to provide such amethod which may be carried out readily and without the necessity ofutilizing more than a minimum of additional equipment.

The above and additional objects of this invention, as well as the novelfeatures thereof, will become apparent from the description whichfollows, when taken in conjunction with the accompanying drawings, inwhich:

H6. 1 is a diagram of apparatus used at the drilling site by which thedata necessary for carrying out the method of this invention isobtained;

FIG. 2 is a reproduction of a portion of a hydrocarbon log produced inaccordance with this invention, covering a depth of 10,420 to 10,600feet, in a well drilled in Reeves County, Tex.;

FIG. 3 is a reproduction of the portions of three types of electricallogs taken in the same well and between the same depths as in FIG. 2;

FIG. 4 is a reproduction of a portion of a hydrocarbon log produced inaccordance with this invention covering a depth of 12,960 feet to 13,040feet in a well drilled in Martin County, TeX.; and

FIG. 5 is a reproduction of an electrical log of the lateral resistivitytype, taken at the same well and between the same depths as in FIG. 4.

Apparatus adapted to carry out the method of this invention, asillustrated in FIG. 1, is utilized with drilling equipment adapted todrill a borehole 1G by means of a drill bit 11, through various strataor formations, such as stratas of sand 12, shale 13, limestone 14 and i5and conglomerate 16. The depth of the borehole will, of course, beconsiderable in comparison with the diameter of the borehole, asindicated by the broken lines between the limestone strata 14 and 15,the distance between which may be on the order of several thousand feet.The drill bit if is attached to the lower end of a drill string 17,consisting of sections of piping of appropriate length, connectedtogether by joints or collars in the conventional manner. The drillstring extends upwardly through a casing 18 and, above the casing, isrotated by a rotary table 19, just above the rig platform 20. The upperend of the drill string 17 is provided with a swivel joint 21, supportedby a hook 22, in turn supported from a conventional drilling rig (notshown). A depth cable 23 is attached to a suitable portion of thesupporing structure for hook 22, extends laterally and then downwardlyover pulleys, as shown, to a depth meter 24, which may be associatedwith a recorder, so as to produce a record of the time at which thedrill bit was at each increment of depth of the well. Incoming mud issupplied through pipe 25 to the top of swivel joint 21 and is pumpeddownwardly through the drill string 17, passes out through the drill bit11 and then moves upwardly within the hole, as indi cated by the arrows.From a point adjacent the upper end of casing 18, the outgoing mud flowsthrough an outlet pipe 26 to a slush pit 27. One or more mud pumps 23,whose suction inlets are disposed in a conventional mixing pit for themud, supplies the mud under the desired pressures to the mud inlet pipe25.

A portion of the mud is diverted from the outlet pipe 26 through a gastrap diversion pipe 30, for passage to a gas trap 31, in which the mudis agitated by a motor driven stirrer 32, and then passes beneath abatfie, as shown, for discharge through a gas trap outlet pipe 33 intothe mud pit 27. .In order to shut oflf the mud diverted to the gas trap31, when desired, a valve 34 is installed in diversion pipe 30, while asample pipe 35 provided with a valve 36 is connected to diversion pipe30. When desired, a mud sample containing a known quantity of specificgases may be suplied to the gas trap, with valve 34 closed and valve 36open, by feeding the same into sample line intake 37, for calibration ortesting of the gas detector and gas chromatograph, referred to below.

It is customary, in installations of this type, to convey the gasseparated from the mud in gas trap 31, as through a pipe 38 and througha branch pipe 39 to a hot wire gas detector 40, connected to a recorder41 by wires 42. Another portion of the gas is conveyed through anotherbranch pipe 43 to a gas chromatograph 44, connected to a recorder 45 bywires 46. At each of hot wire gas detector 40 and gas chromatograph 44,prior to testing, the removed gas is mixed with a predetermined quantityof air, or at any other suitable location between the gas trap 37 andthe testing equipment.

The equipment described above is generally conventional for use inhydrocarbon well logging. Additional equipment for use in carrying outthe method of this invenion includes a flow meter 50, which is installedin the mud outlet pipe 26 and from which extends a lead wire cable 51connect-ed to a recorder 52. A flow meter 53 is installed in the gastrap diversion pipe 30, conveniently adjacent gas trap 31, and isconnected by a lead wire cable 54 with a recorder 55. Another flow meter56, installed in the mud inlet pipe 25 and connected by a lead wirecable 57 with a recorder 58, may be utilized in lieu of, or in additionto, the meter installed in the mud outlet pipe 26. The flow meters 50,53 and 56 may be of any suitable type adapted to measure the flow of mudthrough the respective pipes, one suitable type being the Halliburtonturbine flow meter, which includes a cylindrical flow meter body adaptedto be installed at a relatively short section of the pipe and having inthe body a rotor provided with blades and mounted on a shaft concentricwith the cylindrical body, with longitudinally disposed, radial flowvanes mounted both fore and aft of the rotor, to minimize swirling. Thespeed of the rotor is proportional to the fiow and produces anelectrical impulse or signal at a pick-up mounted centrally atop thecylindrical body, these electrical impulses being transmitted throughthe respective wires to the respective recorders. The recorder chartsare, of course, correlated with time and may be set to automaticallycompensate for the lag time, so that an indication of the flow meterchart for any specific time will correspond with the time at which thedrill bit 11 was at a specific depth, as indicated by the depth meter 24and its associated recorder. Of course, interconnection between thedepth meter 24 and the various recorders may be made, so that each chartwill have a time and depth correlation.

In accordance with this invention, hydrocarbon well logging is carriedbeyond the detection and recording of the relative amount of gascontained in the mud diverted from the outgoing flow line, as practicedsince 1938 by the use of the hot wire gas detector and refined in recentyears by the use of the gas chromatograph, through the followingadditional steps:

(a) Measuring the total volumetric flow of the mud, preferably theoutgoing mud;

(b) Measuring the flow of diverted mud; and

(c) Determining the total relative amount of gas for a selectedincrement of the well bore, for successive selected increments of depthof the Well.

The above method may be further refined by determining the totalrelative amount of gas for a selected volumetric increment of the wellbore, to obtain, rather than a comparative determination which will bedefinitive for any particular well, a comparative determination whichwill be definitive for a number of wells and permit comparison thereof.The above step (c) may be carried out by utilizing a chart, as describedbelow, or through utilization of the ratio between the total mud flowand the diverted mud flow, the amount of gas detected per unit volume ofmud, determining the amount of gas detected from a selected increment ofvolume of the total mud flow, then determining the total gas for aselected increment of the borehole, by utilizing the total volume of mudflow for the period during which such selected increment of the hole wasdrilled. In a refinement of the method, such determination is made moreaccurate, as for comparison purposes between different wells, byintroducing a factor dependent upon the size of the bit and thereforedetermining the total gas for selected successive volumetric incrementsof the well drilled. As will be evident, a principal factor utilized inthe method of this invention is the total hydrocarbon gas detected, asby the hot wire detector, although in a further refinement of theinvention, the amounts of specific gases detected by the gaschromatograph or an equivalent instrument is utilized. Rather thanmaking a determination for each of the gases detected for each incrementof the borehole, the total of the lower hydrocarbons methane, ethane andpropane, hereinafter sometimes referred to as MEP, and the total of theslightly higher hydrocarbons n-butane, isobutane, n-pentane andisopentane, hereinafter sometimes referred to as BP, may be determinedseparately. The results of such determinations are preferably plotted ona log as curves, so as to be correlated with the curve indicating thedrilling time.

Any suitable system of measurement may be utilized, such as the metricsystem, although for the United States and other countries in which asimilar system is utilized, the drilling rate is conveniently measuredin feet per minute, the total rnud flow and gas trap diverted mud flowin gallons per minute, the depth of the well in feet, increments ofdepth of the well in feet and volumetric increments of depth of the wellin cubic feet. As will be evident, for sections of the same or severalwells drilled with the same size of bit, the final determinations willbe directly comparative. However, for different size hits, thedeterminations should be multiplied by a factor corresponding to thesize of the bit, so that the ultimate determinations will be in terms ofcubic feet of hole drilled, rather than longitudinal feet of holedrilled. Thus, the multiplication factors for the various sizes of bitswill be proportioned to 1rD /4 or:

7 For an 8" bit,

For a 9" bit,

f ame For a bit,

For all" bit,

For a 12" bit,

For a 14" bit,

For a 24" bit,

For a 24" bit,

f=a M16 The method of the present invention is based upon therecognition, apparently not perceived for over 25 years, that the mostimportant factor, which determines the a-mout of gas that may bedetected at the surface, is the amount of mud or drilling fluid that hasbeen circulated through a given foot of drilled hole. In principle, themore mud that has been circulated through the bit while one foot of holewas cut, the greater the dilution of the gas that was introduced intothe stream from the foot of formation drilled. The less mud circulatedthrough the given foot of hole will have less dilution and will be moreindicative of the formation producibility. The amount of hydrocarbondetected at the surface from the mud stream is directly determined bythe amount of mud into which the hydrocarbons have been dispersed ordiluted. The drilling rate in minutes per foot times the drilling fluidreturn in gallons per minute will give the total amount of fluid whichcirculated by the formation for any given foot of drilled hole. This isthe amount of fluid that the hydrocarbons of the drilled foot weredispersed into and is the dilution factor that directly deteriines theamount of hydrocarbons that will be detected at the surface in thedrilling fluid.

Not only does the present method provide a positive correlation of wellinformation from one well to another in the same field or nearby areaand allow the operator to compare, in a wildcat well, a new zoneencountered with on at a shallower depth in the same well, but alsoestablishes, apparently for the first time, a definite correlation ofhydrocarbon mud logs from one logging company to another in nearbylocations or areas. Furthermore and quite unexpectedly, hydrocarbon welllogs prepared in accordance with the present invention have a definitecorrelation, in critical areas, with electrical logs taken in the samewell at the same depths and therefore are indicative of the resultswhich would be secured if electrical logs were obtained. This is not tosuggest that electrical logs can be dispensed with, but only to indicatethat significant information, previously secured by electrical logsonly, can be obtained through the hydrocarbon well log. One of thesignificant abilities of such a hydrocarbon well log is an indication ofa narrow, possibly producing zone, hitherto ditlicult, if notimpossible, to determine from previous hydrocarbon logs. This is all themore surprising, in View of the tendency for cuttings to migrate fromone portion of the mud to another While moving up the bore. However, itis possible, although not definitely established, that the cuttings losea large proportion of gas to the mud, either adacent the drill bit orwithin the first few feet, perhaps a hundred or more, above the drillbit. In any event, the most significant characteristic of suchhydrocarbon well logs is an indication of an effective hydrocarbonrelease zone when the curve of total gas per foot of hole or per cubicfoot of hole goes opposite to the drilling rate curve, as will beevident from the hydrocarbon well logs illustrated in the drawings.

PEG. 2 is a hydrocarbon well log, prepared in accordance With thisinvention, for a depth of 10,420 to 10,620 feet, in a well drilled inReeves County, Tex. It contains, in columns from left to right, thedrilling rate curve, the lithology determined from the cuttings, i.e.,limestone at the left and shale at the right, with the depthsuperimposed thereon for convenience, in the center, the total gas curve6%, i.e., total gas per foot of hole, as a dotted line, a solid linecurve 61 based on MEP per foot of hole, another solid line curve 62based on BP per foot of hole, and a column at the right showing tests ofthe mud for weight, viscosity, pH, salinity, and other data, such as theappearance of the cuttin s. The drilling rate curve and the total gascurve are based on determinations made in accordance With thisinvention, as in Table I below.

TABLE I Depth Drill Total Total Trap Trap Total, Total,

Bate, Mud Mud, Flow, Gas, Gas/ Gas/ Frorn T0 Min/Ft. Flow, Gad/Ft.G.p.111. Total Gal. Ft. Hole Gpm.

TABLE I-'C0nt1nued Depth Drlll Total Total Trap Trap Total, Total, Rate,Mud Mud, Flow, Gas, Gas] Gas/ From- To- Min/Ft. Flow, Gal/Ft. G.p,m.Total Gal. Ft. Hole G.p.m.

In the above Table I, the figures in column 4 are the 4 and 7, each forthe corresponding depth. As will be product of the figures of columns 2and 3, column 7 is noted, the figures of column 8 are plotted as thetotal gas the figures of column 6 divided by the figures of column curve60. Curves 61 and 62 of FIG. 2 are plotted from the 5, and column 8 isthe product of the figures of columns 75 additional determinations inTable II below.

TABLE II Depth MEP/ MEP/Ft. BP/ BP/Ft.

Gal. Hole 13 P Gal. Hole Fron1 'Io- In the above Table Ii, the figuresin column 9, MEP, are the totals of methane, ethane and propane detectedby the gas chromatograph, while the figures in column 12, Le. BP, arethe totals of n-butane, isobutane, n-pentane and isopentane, alsodetected by the gas chromatograph. As will be evident, the readings ofthe gas chromatograph are not obtained as frequently as those of the hotwire gas detector, so that Table II does not contain data for as manyspecific feet of depth of the hole as does Table I. In Table II, columns10 and 13 are the figures of columns 9 and 12, respectively, divided bythe figures of column 5 of Table I, while columns 11 and 14 are theproduct of figures of columns 10 and 13, respectively, and column 4 ofTable I. As will be evident, the figures of column 11 are plotted as theMEP curve 62 of FIG. 2, while the figures of column 14 are plotted asthe BP curve 61 of FIG. 2, but to different scales, that for curve 61being the 0 to 800 scale and for curve 62 being the 0 to 200 scale. Itwill also be noted that the total gas curve 60 is plotted on the 0 to200 scale, but multiplied by 1,000, and that the total gas trap readingsof column 6 of Table I are on a different scale from the MEP and BPreadings of columns 12 and 10, respectively, of Table 11. Theseditferent scales do not affect the results secured, since thesignificant aspects of these curves is the curve direction, includingincreases and decreases, and particularly when compared with thedrilling rate curve. As will be evident, the determinations made inaccordance with this invention may be plotted as curves or points ofcurves on a hydrocarbon well log, as in FIG. 3, for correlation with thedrilling rate curve or points of a curve, thereby correlating the samewith the drilling rate.

On the log shown in FIG. 2, there are several indications of zones,possibly productive of hydrocarbons, albeit gas producing zones. Thus,the arrows 63 through 73 and the oppositely directed arrows adjacent thedrilling rate curve, indicate positions at which the total gas curveextends in the opposite direction from the drilling rate curve at depthsof 10,428 ft., 10,433 ft., 10,458 ft. 10,474 ft, 10,483 ft., 10, 189ft., 10,516 ft., 10,544 ft., 10,552 ft., 10,554 ft., and 10,558 ft.,respectively. When this factor is combined with a marked increase in MEPcurve 61 at 10,433 ft., i.e., arrow 64, and between 10,540 ft. and10,560 ft., i.e., arrows -73, the zone is indicated to be a possibly gasproducing zone. It will be noted that the BP curve 62 does not have anysudden increases as does the MEP curve 61, although when a possibly oilproductive zone is encountered, the BP curve 62 should show a markedincrease. It will be noted that the total gas curve 60 goes off thechart at 10,434 ft. and also at 10,596 ft, as will be evident from TableI, while the MEP curve 61 goes otl the chart between 10,546 ft. and10,566 it, as will be evident from Table II.

Referring now to FIG. 3, which, from left to right, contains a laterallog, gamma my log and sonic log, made in the same well for the samedepth as in FIG. 2, it will be noted that a gamma ray log delineates thetype of formation and corresponds generally to the drilling rate curve,while the sonic log gives an indication of porosity. Quite unexpectedly,the curve 60 of total gas per foot of hole of FIG. 2, correspondsgenerally to the sonic electric 10g of FIG. 3. Also, it will be notedthat the arrows 63 to 73, inclusive, of FIG. 3, directed toward variouspoints on the sonic 10g, and corresponding arrows directed. toward thegamma ray log, indicate positions at which the sonic log and the gammaray log extend in opposite directions. As will be noted, arrows 63 to 73of FIG. 3 are at approximately the same depths as arrows 63 to 73 ofFIG. 2. A lateral log, as in FIG. 3, corresponds generally to the gammaray log, but gives a better indication of breaks between differentformations, such as between shale and limestone, or vice versa. However,the peaks and valleys of the lateral log extend in the oppositedirection to the peaks and valleys of the gamma ray log, so that thegamma ray log is more readily compared with the sonic log, to determinepoints or areas in which the curves extend in opposite directions.

FIG. 4 is the drilling rate curve and the total gas detected per cubicfoot of mud, for a depth of 12,960 ft. to 13,040 ft. in a well drilledin Martin County, Tex. The total gas curve of FIG. 4 is based upon adetermination made in accordance with this invention, as shown in TableIII below, in which columns 1 through 8 have the same meaning as inTable I, except that column 8 represents total gas per cubic foot ofhole, rather than longitudinal foot of hole, with a 6 inch bit.

TABLE III Depth Drill Total Total Trap Trap Total, Total Rate, Mud Mud,Flow, Gas, Gas/ Gas/ Cu. From- To- MinJ Ft. Flow, GaL/Ft. G.p.m. TotalGal. Ft. Hole G.p.m.

TAB-LE III- Contin'ued 1 2 a 4 5 6 7 8 Depth Drill Total Total Trap TrapTotal, Total, Rate, Mud Mud, Flow, Gas, Gas/ Gas/ From- To- MirL/Ft.Flow, GaL/Ft. G.p.m. Total Gal. Ft. Hole G.p.m.

The total gas per cubic foot of hole, or total gas per foot of hole, mayalso be determined through use of a chart, such as the chart entitled,Nomograph for Hydrocarbon Well Logging, by Olan T. Moore.

As will be evident, at the points on 'FIG. 4 indicated by arrows 85through 90 and oppositely directed arrows at corresponding positionsadjacent the drilling rate curve, the total gas curve extends in theopposite direction at depths of about 12,977 ft., 12,998 ft. 13,004 ft,13,010 ft, 13,027 ft. and 13,032 ft. Also, the relatively widevariations on the total gas curve, including the positions at arrows 86,87 and 88, as compared with the relative steadiness of the drillingrate, indicate that the entire area from 12,997 ft. to 13,010 ft. may bea producing zone. However, the variations in the drilling rate in thatgeneral area indicate that at arrow 85, there may be a narrow producingzone, while a broader but still relatively narrow producing zone isindicated at the position of arrows 89 and 90. A resistivity microlog isrecorded with electrodes which are mounted a relatively short distanceapart on an insulating pad which is pressed against the wall of thedrill hole. It is used primarily to determine the permeable beds inthose areas where hard or well consolidated formations are predominant.In the resistivity microlog of FIG. 5, the points or curve portions tothe right are indicative of a tightness or greater density of theformation, while the points or curve portions to the left are indicativeof porosity or lesser density of the formation. The formation throughwhich the well of FIGS. 4 and 5 was drilled, between the depthsindicated, was a fairly tight limestone, as determined by lithology (notshown). On the resistivity microlog of 'FIG. 5, taken in the same wellat the same depths as FIG. 4, the points 92, 93, 94 and 97 correspond tothe position of arrows 85, 86, 87 and 90. The broad point 95corroborates that the producing zone may extend to 13,020 ft, while thebroad point 96 is quite close to arrow 89. A producing oil well is nowin operation by the setting of casing and perforations over the areacorresponding to arrows 86 to 90 of FIG. 4.

In the above, it has been assumed that the total mud flow will vary fromtime to time, even though the amount of diverted mud may remainsubstantially constant, and 'that therefore a factor dependent upon thevariations in the total flow of mud should be considered. However, thereare numerous wells in which the total mud flow remains substantiallyconstant over long periods of time,

Drilling time (ft./min.)

Total mud flow (g.p.m.) Trap flow (g.p.rn.)

Gas reading= Gas per ft. hole When changes in bit size are to beconsidered and a factor corresponding to a conversion of the borehole infeet to cubic feet is introduced, the above formula may be expressed asfollows:

Drilling time Total mud fiow (g.p.m.)

(ft/min.) Trap flow (g.p.m.)

Gas reading Hole conversion (ft. to cu. ft.)

=Gas per cu. ft. hole As will be evident from each of the aboveformulae, if the total mud flow and the trap flow remain constant, then,for the first formula above, the product of the drilling time and thegas reading will reflect any variations in the gas per linear foot ofhole, while if the hole conversion factor, i.e. bit size, also remainsconstant, then the product of the drilling time and the gas reading willagain reflect any variations in the total gas per cubic foot of hole.

In view of the fact that numerous wells are drilled during long periodsover which the total mud flow remains constant, the relative amount ofgas per foot of hole or per cubic foot of hole may be determined, in arelative manner, by utilizing the product of the total gas reading andthe drilling time. Of course, the relative amount of MEP per foot orcubic foot of hole, as well as the relative amount of BP per foot orcubic foot of hole, is also desirably determined. For comparison betweenvarious holes, a factor corresponding to the total mud flow divided bythe diverted mud may be introduced. For a number of wells drilled in anarea, it is common to use the same size of bit down to or between thesameldepths in each borehole. Thus, when a comparison is to be made withanother well which has a similar or identical bit program, then it isunnecessary 15 to consider variations in the diameter of the hole, dueto the bit size. Of course, if any well is to be compared with anotherwell which does not or did not have the same bit program, then factorscorresponding to the bit size should be introduced.

Although a preferred embodiment of apparatus adapted to be utilized incarrying out the method of this invention has been illustrated anddescribed, it will be understood that numerous other types of equipmentmay exist. Also, it will be understood that variations, changes andmodifications may be made in the method of this invention withoutdeparting from the spirit and scope thereof.

What is claimed is:

1. A hydrocarbon well logging method for a well drilled by a bit throughsuccessive formations, wherein:

a mud is passed downwardly from the well site to the bit and thenupwardly to the surface and, in passing upwardly, carries with itcuttings produced by the action of the bit and hydrocarbon gases passingfrom the cuttings into the mud and any hydrocarbon gases seeping intothe mud from a formation drilled through;

a portion of the mud discharged at the well site is diverted and gasesare separated from the diverted mud;

the depth of the well is measured in increments and the rate of drillingis also measured; and

the gas separated from the diverted mud is tested for the total relativeamount of a selected number of hydrocarbon gases, said methodcomprising, in addition:

measuring the total flow rate of mud;

measuring the flow rate of diverted mud; and

correlatively recording, for successive selected increments of depth ofthe well, the total relative amount of gas for the mud flowing throughincrements of the well bore at such depths, whereby to obtain therelative gas content of each volumetric increment of the formationthrough which the well is drilled.

2. A method of hydrocarbon well logging, as defined in claim 1, wherein:

the outgoing total flow of mud is measured.

3. A method of hydrocarbon well logging, as defined in claim 1, wherein:

the incoming total flow of mud is measured.

16 4. A method of hydrocarbon well logging, as defined in claim 1,wherein:

said hydrocarbon gases detected include methane, ethane, propane, nbutane, isobutane, n-propane and isopropane. 5. A method of hydrocarbonwell logging, as defined in claim 4, including:

determining, for said successive selected increments of depth of thewell, the relative amount of the total of methane, ethane and propanedetected for said selected increments of the Well bore at such depths;and separately correlatively recording for said successive selectedincrements of depth of the well, the relative amount of the total ofn-butane, isobutane, n-pentane and isopentane for said selectedincrements of the well bore at such depths. 6. A method of hydrocarbonwell logging, as defined in claim 1, including:

determining, for successive increments of the well drilled, the volumeof the formation drilled through; determining, for successive incrementsof the well drilled, the amount of such hydrocarbon gas detected for aselected volumetric increment of the total mud flow; and correlativelyrecording therefrom said hydrocarbon gas detected for the total and mudflowing through selected successive volumetric increments of the ,Well.7. A method as defined in claim 1, including correlating said drillingrate with said determination of the relative amount of detected gas forsaid selected volumetric increment of well drilled.

References Cited UNITED STATES PATENTS 2,214,674 9/1940 Hayward 73-1532,280,075 4/1942 Hayward 73l53 X 2,341,169 2/1944 Wilson et al. 73l532,528,882 11/1950 Hayward 73-153 3,069,895 12/1962 Burk 7323.1

JAMES J. GILL, Primary Examiner.

RICHARD C. QUEISSER, Examiner.

JERRY W. MY RACLE, Assistant Examiner.

